What is a ketogenic diet?

A diet that consists of very low amounts of daily carbs has been called the ketogenic diet. When we eat, for example, 50 grams per day the body starts producing ketones. The liver “burns” fats and creates ketone bodies as byproducts. Ketone bodies can be used as fuel, and the brain will start to rely on ketones rather than glucose.

“One of the common metabolic changes assumed to take place when a person follows a low-CHO diet is ketosis (formation of ketone bodies). Ketone bodies (acetone, acetoacetate, and b-hydroxybutyric acid) are by-products resulting from a partial oxidation of fatty acids in the liver” - Adam-Perrot et al., 2006

“Ketone bodies are produced by the liver and used peripherally as an energy source when glucose is not readily available. The two main ketone bodies are acetoacetate (AcAc) and 3-beta-hydroxybutyrate (3HB), while acetone is the third, and least abundant, ketone body. Ketones are always present in the blood and their levels increase during fasting and prolonged exercise. “ - Laffel, 1999

“... the CNS cannot use fatty acids as an energy source (because they do not cross the blood-brain barrier), thus glucose is ordinarily the sole fuel for the human brain [24]. After 3–4 days of fasting or a very low carbohydrate diet the CNS needs an alternative energy source [19,20,21,22] and this is derived from the overproduction of acetyl-CoA which leads to the production of so-called ketone bodies (KB): acetoacetate (AcAc), β-hydroxybutyric acid (BHB) and acetone.” - Paoli, 2014

“Ketone bodies are fuels endogenously produced by the body from mobilised fat in response to a variety of physiological [21] or pathological conditions [22]. Ketone bodies, acetoacetate (AcAc) and D-β-hydroxybutyrate (βHB), are respiratory fuels that can be oxidised by most body tissues [21] and are formed in large quantities (up to 150 g/day) by the liver in response to low blood glucose and insulin [23, 24].” - Cox and Clarke, 2014

What are ketone bodies?

The three ketone bodies are:

Acetoacetate (AcAc)

β-hydroxybutyric acid (BHB)

Acetone

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How does the ketogenic diet burn body fat?

Some claim that keto burns body fat because it reduces the amount of carbs you eat. Supposedly, the drop in insulin and a rise in ketone bodies leads to fat loss. However, we found no correlation between BHB and weekly fat loss in this article. There is typically no difference in fat loss between keto and other diets as long as calories are matched.

Therefore, the ketogenic diet works similarly to other diets because it reduces the amount of calories you consume.

But doesn’t the ketogenic diet burn more fat?

Yes, the ketogenic diet leads to greater fat oxidation due to fat adaptation. The body uses the energy that is available and will adapt its metabolism depending on what we eat. Yet, greater fat oxidation does not imply that greater body fat loss will occur with the ketogenic diet.

Who is the ketogenic diet good for?

The ketogenic diet is a good choice for losing body fat, even if it isn’t superior to other calorie restricted diets. One of the diet’s advantages is that it’s simple: limit carbs and eat foods rich in fats and protein. This can lead to fat loss without you having to count calories. Some people might have an easier time adhering to the diet.

Should anybody avoid the ketogenic diet?

Athletes should be careful with the ketogenic diet. Athletic performance typically drops in the first weeks of keto, though it slowly recovers over time. The scientific evidence is mixed, but most studies suggest that keto is inferior to other diets in terms of maximizing strength, race performance, and anaerobic performance.

Anybody with diseases/illnesses such as epilepsy, diabetes, and cancer should consult their doctor before starting the ketogenic diet.

Can bodybuilders use the ketogenic diet?

Yes, though it is critical to

eat enough protein (1.6-2.2 grams per kg bodyweight)

do strength training

Note that the ketogenic diet depletes muscle glycogen and water stores. This will have an impact on your body weight, but also on muscle size (muscles shrink due to loss of wet mass). There aren’t ketogenic studies on bodybuilders yet.

How is the ketogenic diet different from the Atkins diet?

The Atkins diet starts as a very low carb diet and is similar to keto in that regard. Yet, with Atkins, you are supposed to reintroduce more carbs after an initial ketogenic period/phase. This means that you might exit ketosis after a while on the diet.

With the ketogenic diet, the goal is to stay in ketosis.

Note that both diets can lead to similar fat loss, and staying in ketosis isn’t a requirement for optimal fat loss.

Which foods are ketogenic?

The total amount of carbs you eat daily determines if you are in ketosis or not. Foods that contain very little carbs, such as vegetables and meat, can be described as ketogenic. Yet, they don’t create ketosis by themselves. Notably, eating a lot of fat does not initiate ketosis.

It is more helpful to talk about the diet as a whole when discussing ketosis, because no single food will “cause” ketosis. It’s the absence of a macronutrient (carbohydrates) that makes the food “ketogenic”. The term “ketogenic foods” might be a misnomer in this sense. A “ketogenic diet” is much more accurate.

With the ketogenic diet, foods that contain large amounts of carbs should be limited or avoided.